Process for bleaching pulp



June 8, 1937. c v s 2,083,294

PROCESS FOR BLEACHING PULP Filed May 16, 1952 INVENTQR I ranci-s czcirvea ATTORNEY Patented June 8, 1937 NITED STATES PATENT OFFICE PROCESS FOR BLEACHING PULP Francis J. Cirves, Manistee, Mich.

Application May 16, 1932, Serial No. 611,692

2 Claims.

This invention relates to a process for bleaching pulp.

An object of the invention is the provision of a process for bleaching pulp such as wood, rag, 5 hemp, or other fibers by injecting free chlorine into an alkaline solution of the pulp.

A further object of the invention is the provision of -a process for bleaching pulp in which an alkaline re-agent is thoroughly mixed with the g pulp and free chlorine is injected into the mixture at the point of greatest agitation.

A further object of the invention is the provision of a process for bleaching pulp in which an alkaline re-agent is mixed with the pulp and 5 during the beating action free chlorine is injected into the mixture at the point of greatest agitation for producing a nascent hypochlorite bleaching compound in direct contact with the fibers. A

This invention will be best understood from a consideration of the following detailed description, in view of the accompanying drawing forming a part of the specification; nevertheless, it is to be understood that the invention is not confined to the disclosure, being susceptible of such -changes and modifications in which define no material departure from the salient features of .the invention as expressed in the appended claims.

In the drawing:

Figure 1 is a horizontal section of a battery beaters, and

Figure 2 is a vertical section of a bleacher showing the application of the free chlorine adjacent the agitators or propellers.

Referring more particularly to Fig. 1 of the drawing, H] designates a typical beater which is semi-circular at its ends in order to provide for the free circulation of the 'pulp. This type of 40 heater is provided with a bed plate (not shown) 45 tainer I0 so that there will be suflicient space to provide for the circulation of the pulp between the ends of the feather and the opposite ends of the container. It will be noted that this feature is hollow for a purpose which does not concern the present invention.

' A beater roll, generally designated by the numeral I3, is cylindrical in form and is secured to' 55 a shaft l4 driven by a pulley l5 from a suitable source of power which uniformly drives the shaft l4 and the beater I3. It will be noted that the beater is provided with blades l6 which are adapted to come in contact 'with the fiber adjacent the bed plate in order that the fibers will be brushed and hydrated and also circulated along the path' thebranch pipe 23 is adapted to inject the chlo-.

rine into the mass within the container Ill at a point adjacent the beater roll [3 so that the chlorine will be injected into the mass at the point of greatest agitation. A valve 25 controls the flow of the chlorine to each container while the valve 22 controls the flow of the chlorine to the branch pipes 23.

Figure 2 is a vertical section of a. type of pulp bleacher. This consists of a cylindrical tank 30 with a circular and sloping bottom 3| and 32. A top 33 forms a closure for the tank.

A pipe 34 enters the upper part of the tank 30 and provides means for supplyingthe tank 30 with the pulp. A pipe 35 is connected with the bottom of the tank and provides a discharge outlet for the pulp after it has been treated with an alkaline re-agent and bleached. A cylinder 36 is located centrally and vertically of the container 30. The opposite ends of the cylinder are open to provide for the inlet and discharge of the pulp.

A shaft 31 driven in any suitable manner (not shown) extends vertically and axially of the cylinder '36 and is provided with propellers 38 spaced at distances along the interior of the cylinder 36. A pipe 39, which is formed preferably of hard rubber, extends through the'top 33 and terminates at 40 within the cylinder 36 while' the outer end 4| is connected with a tank for supplying the pipe with chlorine either in the form of a gas or liquid. A valve 42 controls the admission of the chlorine to the nozzle 40.

The top 33 is provided with an opening 43 through which the lime or soda is inserted for creating an alkaline condition of the pulp as Will be presently explained.

It is to be understood that all of the parts of the device shown in Figs. 1 and 2 are formed of suitable material which will resist the action of the chlorine or certain parts may be formed of glazed tile or lined with a hard rubber coating or covered with a chlorine proof paint.

The operation of my device is as follows: The pulp is placed in the heaters and agitated in order to thoroughly break up the fibers and maintain them in a separated condition and an alkaline re-agent is supplied to the pulp at the proper time -in an amount which approximates from 2% to 25% of the weight of the pulp. It

' will be appreciated that the amount of alkaline re-agent supplied will depend upon the type of pulp employed and the type of paper to be prounderstood as being either an oxide or hydroxide or a carbonate of one of the four elements such as calcium, sodium, potassium, or magnesium.

The alkaline re-agent is thoroughly mixed with the pulp after which the valves that control the flow of the chlorine to the containers are opened.

permitting the chlorine to be injected into the mixture or circulating mass at points of greatest agitation. In other words, the chlorine is injected at points adjacent the beater roll in any of the forms of the heaters which may be em- .ployed so that the chlorine is thoroughly mixed with the pulp and alkaline re-agent where it will act upon the alkaline re-agent and form a hypochlorite bleaching compound in a nascent state and thus the compound will be more effecbleach operation are: (1) The intimacy of con-.'

tive to produce the proper degree of bleaching. These compounds are introduced directly into the pulp and may be used singly or in combination at varying percentages. As stated above from 2% to 25% of the alkaline bleach forming compounds to the weight of bone-dry stock are employed, the percentagedepending uponv the lightness of the bleach stock to be obtained. The alkaline compounds are introduced in dry or powdered form, or'in solution, or in suspension withv water. jected either in a gaseous or liquid form and the amount of chlorine varies from 2 to 25%, depending upon the degree of bleaching to be obtained. The chlorine may be introduced in a water solution. k

The pulpis bleached at high or low consistency at any prescribed temperature or at any ailkaline or pH control. The alkaline bleach forming the ingredients and chlorine are appor tioned to produce the maximum effects of bleached qualities and physical strength characteristics, depending upon the variable conditions of consistency, temperature, alkaline pH and the kind of stock employed.

The bleaching process is especially adapted for the single stage, although several similar stages may be employed. The bleach or process is equally well adapted to the continuous or discontinuous or batch method.

In the discontinuous or batch method,.the bleaching process is formed in a receptacle similar to a bleacher of several tons capacity, as shown in Fig. 2, which is regularly employed in the bleaching of pulp with the use of'prepared hypochlorite bleaching solution. The bleacher should be concrete or stoneware or of other construction which is proof against the action of chlorine. The agitating propeller must be protected by rubber or other chlorine-proof covering or coating. The lime or soda is introduced into the bleaching receptacle with thestock and Y tact of the fibers and the reactive bleach forming constituents, (2) the increased activity of The free chlorine may be infurther treatment "may ,be advisable.

bleaching agent upon the fibers which are chlorinated and immediately and directly exposed to bleaching, (3), the formation of 'nascent hypochlorite bleaching compound in contact with the fibers, (4) the beneficial action of agitation upon the simultaneous -re-action of chlorination and oxidation, (5) the ease of bleaching at ordinary or low temperatures, (6) the beneficial color and strength eifects obtained on the fiber, and (7) the rapidity, economy, and ease of obtaining a ,maximum bleach in one stage operation.

The use of hydrated lime and liquid chlorine is particularly well adapted to the above-described process of bleaching. The amount of lime incorporated in the pulp depends upon'the degree of bleach desired and is practically 50% over the desired chlorine consumption. A specific instance for semi-bleaching will be'appro'xi-' mated by 9% of hydrated lime and 6% ofchlorine by weight to the bone-dry stock. This process is particularly adapted to the use of alkali thoroughly mixed with the pulp according to an established relationship between the desired chlorine consumption and theamount of alkali to be incorporated. This has been determined -as approximately 1.5 to the weight of the chlorineto be consumed where the alkali used is hydrated limeor caustic soda. This enables proper control of the alkali, chlorine and the desired bleach. The process and the control Further processing or refinements in bleaching may be made with the above process but to obtain a desired whiteness or pH of bleached stock Alkali traces in the bleached product caused by impurities or otherwise may be counteracted with slight additions of dilute acids, such as-hypochlorous acid, chlorine water, or a hyp'ochlorite solution. Sulphuric acid, hydrochloric acid, or

.. oxalic maybe employed for counteracting the alkali traces.

I claim: I

l. A process of bleaching pulp for the manufacture of paper which comprises thoroughly mixingfibrous pulpwith hydrated lime and then injecting free liquid chlorine into the mixture of the pulp and lime while the mixture is being agitated, the quantity of chlorine injected being from two to twenty-five percent of the weight of the pulp, the approximate proportions of chlorine and lime being 1 to 1.5 so that an alkaline condition will be maintained. during the bleaching action.

21 A process of bleaching pulp for the manufacture .of paper which comprises beating fibrous pulpin a restricted space while maintaining circulation of the pulp, adding an alkaline re-agent to the pulp and thoroughly mixing the re-agent with the pulp by the beating action, and then injecting liquid chlorine into the mixture at a point where the pulp is being beaten so that the chlorine will be thoroughly mixed with the pulp P and alkaline re-agent, the approximate proportions of chlorine and lime being 1 to 1.5 so that an alkaline condition will be maintained during the bleaching action.

FRANCIS 'J. CIRVES. 

